Solar monitoring system for measuring solar radiation intensity

ABSTRACT

A solar monitoring system for measuring solar radiation intensity comprising a tracking unit having two-axis movement comprising, an image capturing head mounted with first and second irradiation measuring units, and a controller. The first irradiation measuring unit comprises a direct normal irradiance (DNI) sensor and the second irradiation measuring unit includes a diffuse horizontal irradiance (DHI) sensor and a global horizontal irradiance (GHI) sensor. The controller receives inputs from the sensors or a software program configured to control orientation of the image capturing head so that the DNI sensor is always exposed to the sun, and the shading disc is always directly between the DHI sensor and the sun.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Indian patent application No. 201641025797 entitled “SOLAR MONITORING SYSTEM FOR MEASURING SOLAR RADIATION INTENSITY” filed on Jul. 28, 2016.

FIELD OF THE INVENTION

The present invention relates to a solar monitoring system for measuring the solar radiation intensity used in solar energy systems. The invention also relates to a solar tracking mechanism for accurately pointing particular sensors directly at the sun.

DESCRIPTION OF THE RELATED ART

In this era of increasing energy demand and shortage of conventional energy resources, solar energy is a renewable energy source that is increasingly becoming cost-competitive. Solar energy systems convert solar radiation into one or the other forms of energy which can be readily used, such as heat or electricity. One of the primary needs in assessing a site for such energy system is to accurately measure and analyze the solar radiation characteristics at the given location. An accurate measurement of the solar radiation is required to determine the feasibility of harnessing solar energy at that site. In addition, the values of solar radiation for a particular site are highly variable and change significantly with the time of day, time of year, weather, and other parameters. There are three main types of solar radiation, which are commonly measured and utilized: DNI (Direct Normal Irradiance), DHI (Diffuse Horizontal Irradiance), and GHI (Global Horizontal Irradiance).

Direct normal irradiance (DNI) is the solar radiation directly received from the sun falling on a square unit area of a surface whose normal (perpendicular to a given object) is always pointing to the sun. Most concentrating solar thermal energy systems can only utilize DNI radiation. Thus, it is very important to measure this parameter independently. Pyrheliometers are commonly used to measure this value. In order to continuously measure the solar radiation coming directly from the sun, the pyrheliometer must track or follow the position of the sun, which is constantly changing throughout the day and year, with a high degree of accuracy.

Diffuse horizontal irradiance (DHI) is the radiation measured on a horizontal plane which is not directly from the sun. It is a measure of only the solar radiation that has been reflected off various surfaces such as clouds, the ground, buildings, etc. A pyranometer is typically used to measure this value. However, the sunlight which comes directly from the sun must be blocked by using shading devices such as shading ring or a shading disc, which is placed in front of the pyranometer. As the position of the sun is constantly changing in the sky, the shading device must move to track or follow the sun with a high degree of accuracy, such that the shading device is always directly between the sun and the pyranometer, and always casting a shadow over the pyranometer. Global horizontal irradiance (GHI) is the overall radiation intensity measured on a horizontal unit area, provided the radiation is coming from the entire dome of the sky. It is measured using a pyranometer and measures total solar radiation, both direct and diffuse, incident on a horizontal, non-tracked surface. This information is especially useful for solar PV installations.

Comprehensive solar measurement system for an accurate assessment of the solar energy potential at a site must measure the DNI, DHI, and GHI radiation over a period of time, either diurnal or seasonal cycles or both. This requires a solar-tracking pyrheliometer, a horizontal pyranometer with a solar-tracking shading device, and a horizontal unshaded pyranometer. Other sensors or combinations of sensors with similar capabilities to the pyrheliometer and pyranometer can also be substituted respectively, without loss of functionality.

Most of the systems on the market for measuring comprehensive solar radiation for direct normal irradiance (DNI), diffuse horizontal irradiance (DHI) and global horizontal irradiance (GHI) are expensive and complicated in design. They employ either parallelogram, four-bar linkages to control the shading disc, such as the Kipp and Zonen Solsys sun tracker, or employ a shading ring, such as the Eko instruments RSR-01 shadow ring. These systems have the disadvantage of blocking more diffuse radiation than intended. Further, they are designed to be constructed with a greater number of moving parts, with associated disadvantages.

The present disclosure addresses some of the drawbacks of conventional methods and satisfies the need for a system that is simpler in construction, cheaper, more reliable, less prone to wear and tear, and more accurate for measuring the solar radiation, with further related advantages as set forth here.

SUMMARY OF THE INVENTION

In one aspect, the invention discloses a solar monitoring system for measuring solar radiation intensity. The system comprises a tracking unit having movement about an azimuth axis and an elevation axis comprising an image capturing head mounted with first and second irradiation measuring units. The first irradiation measuring unit comprises a direct normal irradiance (DNI) sensor and the second irradiation measuring unit includes a diffuse horizontal irradiance (DHI) sensor and a global horizontal irradiance (GHI) sensor affixed along the elevation axis.

In one aspect of the system, the diffuse horizontal irradiance (DHI) sensor further comprises a shading disc masking direct solar exposure thereon. Further, a controller that receives inputs from the sensors of irradiation measuring units or a software program and is configured to control orientation of the image capturing head so that the DNI sensor is always exposed to the sun and the shading disc is always directly between the DHI sensor and the sun. In various embodiments, the image capturing head is a pan-tilt camera head and, the first irradiation measuring unit is a pyrheliometer and the second irradiation measuring unit is a pyranometer. Each sensor may be an optical sensor for measuring the intensity of various radiation parameters of the sun.

In one aspect of the system, the controller is configured to drive motors for the azimuth and elevation axes of rotation of the tracking unit in response to the sensor or software program inputs. The controller further includes a processor, memory, and optional display, and communication hardware. The processor is configured to receive inputs from the sensor and transmit instructions to control the tracking unit based on the sensor inputs according to programmed instructions.

In various aspects of the invention, the controller is configured on a computing device such as a laptop, a wearable computer, an embedded computer, a personal digital assistant (PDA), a mobile phone, a smart phone or a tablet. In one aspect, the controller receives inputs from the sensors via wired or wireless communication. The wireless network operates on a WiFi or an infrared or a Bluetooth or a ZigBee or a similar communication protocol in the system.

In various aspects of the invention, the system further comprises a tilt sensor to identify non-level installation and an electronic compass to determine directional orientation. In one aspect, the tilt sensor and the electronic compass are configured to provide inputs to the controller. The controller is configured to self-compensate for level and directional orientation in positioning the image capturing head.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a solar monitoring system for measuring solar radiation intensity according to one embodiment of the invention.

FIG. 2 illustrates the control system of the solar monitoring device according to one embodiment.

FIG. 3 is a schematic of another embodiment of the control system of the solar monitoring device for measuring solar radiation intensity.

FIG. 4 illustrates an embodiment of the communication architecture for the system for controlling the motor head according to the position of the sun.

FIG. 5 illustrates the server-client architecture for the solar monitoring system used in an embodiment.

Referring to the drawings, like numbers indicate like parts throughout the views.

DETAILED DESCRIPTION

While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on.” Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

The proposed solar monitoring system for measuring solar radiation intensity is further described with reference to the sequentially numbered figures. The solar monitoring system for measuring the solar radiation intensity is used in various aspects of the solar energy system. A solar tracking mechanism with an irradiation measuring unit is used for determining the irradiance from the sun.

In one embodiment the solar monitoring system 100 shown in FIG. 1, includes a tracking unit 101 containing an image capturing head 104 that is movable about an azimuth axis 102 and an elevation axis 103. Image capturing head 104 could be a pan-tilt head that is mounted with first irradiation measuring unit 120 and second irradiation measuring unit 130. In various embodiments, the tracking unit is configured to rotate about the azimuth axis 102 and the elevation axis 103. The first irradiation measuring unit 120 comprises an elongated hollow tube 121 that includes a direct normal irradiance (DNI) sensor 122 affixed inside the bottom of tube 121. The second irradiation measuring unit 130 includes general solar radiation intensity sensors (pyranometers in this embodiment) configured as a diffuse horizontal irradiance (DHI) sensor 131 and a global horizontal irradiance (GHI) sensor 132. Sensors 131 and 132 affixed along the elevation axis 103 have their sensing elements horizontally and aligned on the axis 103, so that together they rotate or pan in the azimuthal or horizontal direction. Therefore, the tracking unit 104 with two single axes tracking the sun's position by means of mutually orthogonal (perpendicular) axes.

In various embodiments, the diffuse horizontal irradiance (DHI) sensor 131 further comprises a shading disc 140 for masking direct solar exposure over sensor 131. As observed in FIG. 1, the shading disc 140 is mechanically affixed to the whole assembly so that whenever sensor 122 is exposed to the sun, disc 140 covers sensor 131 from direct solar irradiance.

The system further includes a controller 150 configured to control orientation of the image capturing head 104 so that sensor 122 always exposed to the sun, and the shading disc is always directly between the sensor 131 and the sun. In one embodiment, the controller 150 receives control input from a Solar Position Algorithm, which could be running in controller 150 or running in an external processor, with control information transferred by a network or communication line to controller 150. These control inputs are used to configure a pair of motors 161 and 162 for rotating the pan/tilt head 104 with respect to the two axes 102 and 103. Henceforth, orientation of the pan/tilt head 104 is controlled in such a manner so that sensor 122 is always exposed to the sun, and the shading disc is always directly between sensor 131 and the sun. In one embodiment, the two axes 102 and 103 of the pan/tilt head 104 are rotated by a motor connected to a harmonic gear head.

As illustrated in FIG. 1, the solar monitoring system 100 in one embodiment comprises two axis movements, about the vertical or azimuth axis 102 and the horizontal or elevation axis 103. In various embodiments, depending on the terrain on which the equipment is located, there may be slight deviation of the azimuthal axis 103 from the vertical, although the axis is intended to have a substantially vertical orientation. Similarly, the elevation axis 102 may slightly deviate from the horizontal. In one embodiment, the system 100 may further include a leveling stage for level mounting of the equipment in uneven terrain. However, the two-axis movement is intended to compensate for minor deviations of a few degrees from level positioning to enable proper functioning of the system. In some embodiments the system 100 may comprise additional sensors (not shown) for identifying the orientation of the system 100, such as an electronic compass, and for self-correcting for non-level installation, such as electronic tilt meters or accelerometers or manually leveling the system, such as tilt meters or levels, may also be built with the system for precisely positioning, installing and calibrating of the system.

In one embodiment, the pan/tilt head 104 may be a pan-tilt (PT) camera head. Alternatively, in one embodiment, the device with the same functionality as the pan-tilt (PT) camera head may be custom fabricated from elements such as motors, gears, and motor driving circuits. The pan-tilt (PT) camera head device constitutes two axis rotational tracking capabilities, which can be moved around to view a larger area. The pan movement of the pan-tilt (PT) camera head device is analogous to azimuth axis 102 of rotation for the tracking unit 101. The tilt movement of the pan-tilt (PT) camera head device is analogous to elevation axis 103 of rotation for the tracking unit 101.

In one embodiment, the first irradiation measuring unit 120 may comprise a pyrheliometer 122 and the second irradiation measuring unit 130 may comprise pyranometers 131 and 132. In one embodiment each sensor 122, 131 and 132 of the irradiation unit 120 and 130 may be any optical sensor for determining the relevant intensity of the sun. The optical sensor converts incident solar irradiation into electronic signals, which measures the physical quantity of light and then translates it into a readable form. In one embodiment, other equivalent sensors to the pyrheliometer and pyranometers for measuring the solar irradiation may also be used, which provide analog voltage signals, proportional to the amount of incident irradiation. In various embodiments, the optical sensors may be chosen based on wavelength, forward (drive) current, acceptance angle, range, power dissipation, packaging type and maximum collector-emitter (CE) voltage and may communicate their readings via analog or digital methods.

In one embodiment as illustrated in FIG. 2, the controller 150 is configured to drive motors 161 and 162 for the two axes 102 and 103 of rotation of the tracking unit 101 (FIG. 1) in response to the sensor inputs. The pan/tilt head 104 (FIG. 1) head have motors 161 and 162 inbuilt, with or without additional gearing. In one embodiment, the pan/tilt head 104 (FIG. 1) may use an encoder such as a magnetic or optical encoder and a potentiometer, or other types of sensors to determine the angular position or amount of rotation in the different directions of rotation. In some embodiments, the controller 150 or 250 uses standard digital protocol such as the PELCO-D, or other standard communications and control protocols. Therefore, orientation of the pan/tilt head 104 (FIG. 1) is controlled in such a manner, so that sensor 122 is always exposed to the sun, and the shading disc is always directly between sensor 131 and the sun.

In one embodiment as illustrated in FIG. 3, the controller 250 may be further connected to a computing device 270 comprising processor 271, memory 272, and display 273, and through a communication network 255 to provide enhanced functionality for remote monitoring and control. In various embodiments, the processor 271 is configured to calculate the sun's position via the Sun Position Algorithm or receive inputs from sensors and transmit instructions to control the tracking unit 101 according to programmed instructions. In various embodiments, the computing device 270 is configured to be a computing device such as a laptop, a wearable computer, an embedded computer, a personal digital assistant (PDA), a mobile phone, a smart phone or a tablet.

In one embodiment, the controller 250 may receive inputs from the sensors via communication network 255 by wired or wireless communication. In one embodiment of the system 100, the operating condition of the more motors 161, 162, 261 or 262 may be controlled in response to instructions received via a manual input, control signal from control unit 150 or 250 or a programmed input from the computing device 270. In various embodiments, the wireless network may operate on a protocol such as WiFi, an infrared, Bluetooth, a ZigBee communication protocol or other similar protocols.

In one embodiment, the computing device 270 may include a GPS receiver 275 to geolocate the system. In this embodiment, the system 100 is configured to orient itself to the sun using a Sun Position Algorithm (SPA) such as given by NREL (National Renewable Energy Laboratories, USA), stored in memory 272 of the control electronic device 270. The algorithm may be configured to compute the precise position of the sun, based on the exact time and location of the system and provide control inputs to the control electronics located within controller 250 so as to accurately orient the pan/tilt head 104 toward the sun. Instead of the GPS sensor, the GPS information could also be entered manually into the device and the necessary sun position calculations performed.

In various embodiments, controller 150 or 250 may use one or a combination of proportional, integral, or derivative control algorithms to ensure that sensor 122 is always pointed directly at the sun, and the shading disc is always directly between sensor 131 and the sun.

While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material the teachings of the invention without departing from its scope. Any other solar monitoring system for measuring solar radiation intensity used in the manner illustrated also falls within the scope of the invention, as further illustrated with reference to the examples below. However, the system can be used in identifying solar radiation intensity for applications in many fields such as agriculture, astronomy, atmospheric study, hydrology, oceanography, and renewable energy. However, the examples are not to be construed as limiting the scope of the invention as defined by the appended claims.

EXAMPLES Example—1: Construction of Solar Monitoring System

The design centers around the use of a conventional camera pan/tilt motor head for the purpose of two axes rotational tracking movements. The solar monitoring system with a standard pyrheliometer, two standard pyranometers, and a shading disc were used for measuring the incident radiation. Design modifications were made to the PT head so as to fit in the pyrheliometer and pyranometer firmly on to the structure.

The sun's position can be completely described as an azimuth angle/elevation angle pair (or equivalent coordinate set which can be proved using a coordinate transform). Therefore, a device with two single axis rotational tracking with mutually orthogonal (perpendicular) axes is used to track the sun's position. One rotational axis should be pointing straight up (normal to the earth's horizontal surface) and the second axis should be in a horizontal direction. The second axis rotates upon the first, such that when the first axis is rotated, the azimuth angle of the device changes, while when the second axis is rotated, the elevation angle of the device changes.

The pyrheliometer is attached to the two-axis device such as to always be pointing towards the sun. This measures the direct normal irradiance (DNI). A shading disc can also be attached to this device such as to always be directly in between a pyranometer fixed to a horizontal plane of this device and the sun. However, the sensing element of this pyranometer must lie on the axis of rotation of the shading disc. This pyranometer will measure the diffuse horizontal irradiance (DHI). A second pyranometer can be attached to the same or any other different fixed horizontal plane of the device. This second pyranometer will measure the global horizontal irradiance (GHI).

Attaching the pyrheliometer to the two axis tracking unit is relatively straight-forward, and attaching two pyranometers to horizontal planes of the device is also straight-forward. However, it can be rather difficult to make a shading disc always lie directly between the sun and one of the pyranometers, regardless of where the sun is at in the sky. Typically, a parallel bar/link mechanism is used to do this, which is a more complicated system. In other instances, a shading ring is used, which blocks a substantial portion of the diffuse radiation which should be measured. However, by locating one of the pyranometers directly on the second, horizontal rotational axis, and fixing the shading disc on an arm extending perpendicular to the second axis, which rotates about the second axis, it can be assured that if the arm is pointing to the sun, then the shading disc will always be directly in between the sun and the pyranometer, for any position of the sun.

The solar monitoring system configured by a pan-tilt motor head relating to its operation. A pan-tilt (PT) camera head is one device on the market which has two axis rotational tracking capabilities. They are typically used to mount a surveillance camera such that it can be moved around to view a larger area. The pan movement of the PT camera head is analogous to azimuth tracking, and the tilt movement of the PT camera head is analogous to elevation angle tracking. The pyrheliometer can be mounted to the tilting part of the PT camera head such that it can always pointing at the sun, when the PT head is properly controlled, giving DNI measurements. A horizontal surface can be mounted with two pyranometer to the panning part of the PT casing.

The pyranometers remain flat at all times, although they do rotate in the azimuth direction, which does not affect their reading. The shading disc is then attached to an arm which is attached to the tilting part of the PT head. This arm reaches over and when the PT head is controlled correctly, the shading disc will always shade one of the pyranometers from direct sunlight, giving DHI measurements. The other pyranometer is always left unshaded and horizontal, giving GHI measurements. In this way, a comprehensive solar measurement system for measuring DNI, DHI, and GHI, is created that uses only a PT camera head and does not use a parallelogram, four-bar linkage or a shading ring.

Example—2: Communication and Network Architecture for the System

In one embodiment, a desktop computer runs Labview software and uses the SUNAE or a similar Solar Position Algorithm to determine the sun's position. The communication architecture used in this system is shown in FIG. 4. Labview provides control signals which are sent over the internet using TCP-IP protocols to a Labjack UE9 Pro data acquisition and control (DAQ) device. The LabJack UE9 Pro sends TTL serial data commands to a Commfront TTL-RS 485 serial converter, which then converts the TTL signals to RS-485 voltage levels to be given to the PT motor head. This establishes the communication between the Labjack and the PT motor head. Labview creates movement commands using the industry standard PELCO-D serial communications protocol.

The Labjack UE9 Pro is assigned with the specific IP address and can be accessed from anywhere using the internet. The Labview software has the web interface module which allows communication to the Labjack. The serial commands were send to the Labjack from the Labview, in accordance with the pre-programmed logic. The server-client architecture used in this system is shown in FIG. 5.

Labview software controls the pan-tilt (PT) motor using the PELCO-D serial commands. It's a seven-byte hexadecimal command structure. The significance of the byte variables used are as follows:

Byte1: Synchronization byte

Byte2: The equipment address

Byte3: Camera functionality

Byte4: Motor head functionality

Byte 5: Motor pan speed

Byte 6: Motor tilt speed

Byte 7: Checksum of the bytes

These seven bytes add up to make the PELCO-D command structure and are serially sent to the pan-tilt (PT) motor head. Bytes 1 through 3 are constants. Bytes 4 through 7 are variables which are being controlled from the Labview program in real time, either by user initiated or program initiated.

Example—3: Pan/Tilt Movements and Tracking Algorithm

Using SUNAE algorithm, the solar position angles at a given location at a given time is calculated. The pyrheliometer pointing direction is kept aligned to these angles, so as to track the sun. The slowest turning speed of the motor head is 0.25 degrees/second. The solar elevation slew rate as per the algorithm is 0.00333 degrees/second. Therefore, in order to track the elevation angle correctly, the motor tilt movement is adjusted by 0.25 degrees every 75 seconds. Similarly, the solar azimuth slew rate as per the algorithm is 0.01666 degrees/second. Therefore, to track the azimuth angle properly the motor pan movement is adjusted by 0.25 degrees every 150 seconds. When the solar elevation is greater than zero degree, the tracking mechanism starts tracking the sun. This tracking is continued until the solar elevation is less than zero degree. The whole tracking mechanism is automatically calibrated back to its starting position at 12.00 am local time.

Example—4: Prototype Solar Irradiance Measurement Unit

The components used for the prototype are tracking unit, pyranometers, pyrheliometers, controller and data acquisition unit. The pan/tilt motor head were used for camera installation purposes. Design modifications were performed to the pan/tilt motor head so as to accommodate the pyrheliometer and the pyranometers. The horizontal and the vertical axis are each rotated by a stepper motor that is directly connected to a harmonic gear head with zero backlash. The controlling and the data acquisition were done with the help of an Ethernet powered data acquisition device, however a wide variety of data acquisition and control systems were implemented.

While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material the teachings of the invention without departing from its scope. 

We claim:
 1. A solar monitoring system (100) for measuring solar radiation intensity comprising: a tracking unit (101) having movement about an azimuth axis (102) and an elevation axis (103) comprising, an image capturing head (104) mounted with first (120) and second (130) irradiation measuring units; wherein the first irradiation measuring unit (120) comprises a direct normal irradiance (DNI) sensor (121) and the second irradiation measuring unit (130) includes a diffuse horizontal irradiance (DHI) sensor (131) and a global horizontal irradiance (GHI) sensor (132) affixed along the elevation axis (102); wherein the diffuse horizontal irradiance (DHI) sensor (131) further comprises a shading disc (140) masking direct solar exposure thereon; and, a controller (150) that receives inputs from the sensors (121, 131 and 132) of irradiation measuring units (120 and 130) or a software program and is configured to control orientation of the image capturing head (104) so that sensor 122 is always exposed to the sun, and the shading disc (140) is always directly between the sensor 131 and the sun.
 2. The system of claim 1, wherein the image capturing head (104) is a pan-tilt camera head.
 3. The system of claim 1, wherein the first irradiation measuring unit (120) is a pyrheliometer and the second irradiation measuring unit (130) is a pyranometer.
 4. The system of claim 1, wherein each sensor (121, 131 and 132) is an optical sensor for measuring radiation intensity of the sun.
 5. The system of claim 1, wherein the controller is configured to drive motors for the azimuth and elevation axes of rotation of the tracking unit (101) in response to the sensor or software program inputs.
 6. The system of claim 1, wherein the controller further includes a processor (151), memory (152), display (153), and communication hardware (155), and wherein the processor is configured to receive inputs from the sensor and transmit instructions to control the tracking unit based on the sensor inputs according to programmed instructions.
 7. The system of claim 1, wherein the controller (150) is configured on a computing device such as a laptop, a wearable computer, an embedded computer, a personal digital assistant (PDA), a mobile phone, a smart phone or a tablet.
 8. The system of claim 1, wherein the controller (150) receives inputs from the sensors via wired or wireless communication.
 9. The system of claim 8, wherein the wireless network operates on a WiFi, infrared, Bluetooth or ZigBee communication protocol.
 10. The system of claim 1, further comprising a tilt sensor to identify non-level installation and an electronic compass to determine directional orientation.
 11. The system of claim 10, wherein the tilt sensor and the electronic compass are configured to provide inputs to the controller (150) and wherein the controller is configured to self-compensate for level and directional orientation in positioning the image capturing head (104). 